This invention relates to valve actuating mechanisms for engines and the like and more particularly to a variable mechanism incorporating a magnetorheological fluid lost motion device.
Variable valve actuation mechanisms have been extensively developed and to some extent utilized to improve engine efficiency by reducing or eliminating throttling losses, improving idle stability and controlling the timing of valve opening and closing to increase engine power and/or to improve engine exhaust emissions. The development of such mechanisms has included both mechanical and hydraulic devices including mechanisms with hydraulic lost motion devices in the valve train. However, these devices have not yet reached wide spread commercial application, possibly due to low temperature viscosity problems which may affect hydraulic system performance as well as the cost of engine modifications to apply suitable hydraulic systems. MRF technology has been applied in various ways to fluid dampers, clutches and brakes, vehicle suspensions and other applications but it is not known to have been developed or applied in engine valve actuating mechanisms.
The present invention provides an improved variable valve actuating mechanism which utilizes magnetorheological fluid (MRF) in lost motion devices applied to a valve actuating system to provide improved variable actuating mechanisms for controlling engine valves and the like.
The present invention is directed primarily to the application of MRF technology to valve actuating mechanisms in which the timing and or lift of valve motion can be controlled by lost motion devices using MR fluids. A number of embodiments of MRF lost motion devices designed for application to engine valve actuating mechanisms are illustrated as examples of how MRF technology may be applied to control valve actuation.
According to the invention, the lost motion devices are designed with either of two operational modes, a direct shear mode and a valve mode. In the shear mode, the MR fluid is retained between relatively movable surfaces of a lost motion device and the relative motion is controlled by varying the shear strength of the fluid by a controlled electromagnetic flux passed through the fluid within the device. In the valve mode, the MR fluid is displaced from one portion of a chamber to another through an orifice. The flow rate through the orifice is controlled by varying the magnetic field so that the effective viscosity of the fluid is varied to control the rate of fluid volume change in the chamber.
The lost motion device units may be applied directly between an input cam and an output valve or may be applied to a pivot for a finger follower or a rocker arm type of valve actuation. Other variations of the application of lost motion devices according to the invention are of course possible.